Drive device for a wind turbine

ABSTRACT

Drive device for a wind mill comprising a large pulley ( 21 ) disposed on a main shaft ( 22 ) and at least one belt ( 27 ) or chain adapted to transfer rotation from the pulley ( 21 ) to a generator ( 30, 31 ). The pulley ( 21 ) is rotationally coupled to at least two secondary shafts ( 23, 24 ), which are disposed parallel to the main shaft ( 22 ). One or more belts ( 27 ), which transfer the rotation, extend over the pulley ( 21 ) and the secondary shafts ( 23, 24 ). The secondary shafts ( 23, 24 ) are in turn rotationally coupled to at least one, preferably two, electric generators ( 30, 31 ).

The present invention relates to a drive device for a wind turbineaccording to the preamble of the following claim 1.

In most of today's wind turbines the drive unit is placed in a nacelle,which also carries the wind turbine rotor. The nacelle is necessarilyarranged on top of a high mast and rotates so that the rotor is alwaysfacing the wind.

Such placement of the drive unit results in a great weight at the top ofthe mast and that access for maintenance is a challenge. Yet it is thisposition of the drive unit and the generators that is used extensivelyas the alternative is that the rotational torque must be transmitted viaa shaft through the mast, something that leads to losses and requiresthat the mast can absorb the reaction torque from the rotating shaft.

There is therefore an urgent need to simplify the drive unit and make itlighter. There is also a need to make access for maintenance easier.These are the main aims of the present invention, and these are achievedby the features that appear in the characterising part of claim 1.

To use a belt to transmit the rotation from the rotor to a generator isknown from, among others, WO 2008/028335 and JP 2005023893. However, thepresent invention aims to utilise the characteristics of the beltoperation, or possibly the chain operation, better so that a morecompact drive device can be achieved with additional operationalbenefits.

Some of the benefits that can be achieved by the invention in relationto the belt operation, according to the known solutions are:

-   -   One gets a doubling of the utilisation of the capacity of the        belts with respect to the known belt operation. This relates, in        particular, to large (and therefore costly) belts and associated        large belt wheels.    -   The structure becomes more compact.    -   The torque over the drive shaft is balanced.    -   The generation of power can be divided onto two generators that        can be open to a more reasonable generator control system.    -   The time before one needs to replace belts can be made longer        because one can drive the torque on a single generator when        there is little wind.

In comparison to traditional drive systems with cogged wheel transfer,or direct operation, one can achieve the following benefits:

-   -   Reduction of shock loads (large momentum changes, vibration,        etc. are dampened).    -   Makes complex lubrication and cooling systems unnecessary.    -   The system will be less prone to corrosion and have lower        maintenance needs. This is particularly relevant for offshore        wind turbines. The belt wheels can, for example, be given a zinc        coating to reduce corrosion, something that is not possible with        cogged wheel transmissions.    -   A weight saving is achieved by integrating the drive shaft in        the belt wheel and also by taking up the torque over a large        radius instead of a small radius inside a gearbox.    -   The number of parts that must be manufactured in the production        of the drive system is significantly reduced.    -   A large part of the maintenance can be done without the use of a        large crane. The belts are most susceptible to wear, but even        the big belts do not weigh more than 70-100 kg. The belt wheel        will not be subjected to wear as the belt is soft.    -   Scaling up to, for example, 5, 7 and 10 MW, will be possible        without the mass of the drive system increasing exponentially.        The mass of a 5 MW turbine with gearbox or direct drive will        quickly become very heavy.    -   The power from the rotor can be distributed to several standard        generators, something which results in increased flexibility.    -   A larger exchange can be brought about in one step than with        cogged wheel transmission. This is because a large exchange in        cogged wheel transmissions leads to high pressure forces on the        cogs, something which results in much wear. With a belt        operation, there will be a softer transmission and some slip may        be acceptable at abrupt torque changes.    -   A belt drive system also has advantages compared with direct        operation. With direct operation a relatively low rotational        speed is transmitted to the generator. This means that the        generator must be large and heavy. At higher rotational speeds        one can use smaller and lighter generators.

The invention shall now be explained in more detail with reference tothe accompanying drawings, where:

FIG. 1 shows a known nacelle for a wind turbine with a rotor hub, adrive unit and a generator.

FIG. 2 shows a nacelle similar to that shown in FIG. 1, but with a drivedevice according to the invention.

FIG. 3 shows the drive device according to the invention in perspective.

FIG. 4 shows the drive device according to the invention in perspectivefrom the opposite side and

FIG. 5 shows the drive device according to the invention in a splitdrawing.

Firstly, the known nacelle according to FIG. 1 shall be brieflyexplained. It comprises a rotor hub 1 to which the wind turbine blades(not shown) are attached. The hub 1 is mounted in a main bearing 2 andis connected to a main shaft 3. The main shaft is connected to a maingear 4. The gear 4 is fitted with a brake 5. The gear is connected to agenerator 7 via a connection 6. The nacelle is also fitted with a swivelbearing 8, swivel gear 9 and swivel ring 10 for rotation of the nacellein relation to a tower 11, on which the nacelle is placed.

The present invention aims to replace the following components in theknown nacelle above: the main shaft 3, the main gear 4, the brake 5 andthe connection 6.

FIG. 2 shows the nacelle in FIG. 1 with the drive device according tothe invention placed at an intended location and with the known nacelleas a background.

However, before FIG. 2 is explained, the drive device according to theinvention shall be explained with reference to the FIGS. 3-5, which showthe drive device according to the invention separate from the nacelle.

The drive device is mounted in a frame 12, which has a first opening 13at the one end that faces away from the hub 1 and a second opening 14 atits other end facing towards the hub 1. The opening 14 is circular andis set up to receive a rotation bearing 15. The frame also includes aload-carrying wall 16 for a main shaft bearing 17. The load-carryingwall 16 is equipped with openings 18 and 19. The frame 12 is designed atthe bottom to take up a swivel bearing for is rotation of the nacelle inrelation to the tower. The frame also has an opening 20 in this area.

A large belt disc wheel 21 is mounted between the swivel bearing 15 andmain shaft bearing 17 with the help of a main shaft 22. Two secondaryshafts 23 and 24 are mounted in parallel with the large belt disc 21 andthe main shaft 22. Each of these is fitted with a small belt disc 25, 26at the ends facing away from the hub 1. A set of belts 27 extends aroundthe large belt disc 21 and the secondary shafts 23, 24 to transmit therotation torque from the large belt disc 21 to the secondary shafts 23,24. The secondary shafts 23, 24 are mounted between brackets 28, 29 atthe side of the opening 14 and the load-bearing wall 16. Two generators30, 31 are attached to the frame 12 and have generator shafts 32, 33that extend through the load-bearing wall 16. These generator shafts 32,33 are in rotational connection with each of the small belt discs 25, 26via sets of belts 34, 35.

The large belt disc 21 is provided with spokes 36 so that four openings37 are formed through the belt disc 21 itself.

The above mentioned results in a compact unit that can form aload-bearing part of the nacelle. FIG. 2 shows how this unit will beplaced in the nacelle. The hub will be connected directly to the largebelt disc 21 by means of a number of bolts that are screwed into thebolt holes 38 in the belt disc 21.

Thus the rotation of the hub will lead to a rotation of the large beltdisc 21. This will in turn be transmitted to the secondary shafts 23, 24via the belts 27 and on to the generators 30, 31 via the small beltdiscs 25, 26 and the belts 34, 35. Since the large belt disc 21 has asignificantly larger diameter than the secondary shafts 23, 24, even asmall rotational speed of the hub will cause a large rotational speed ofthe secondary shafts 23, 24. A very large exchange in one step isthereby achieved.

The parallel and diametrically opposite secondary shafts 23, 24 providea good balance the large belt disc 21. The tightening of the belt can beadjusted by is moving the secondary shafts sideways, as is suggested bythe oblong holes 39 in the brackets 28, 29 and the load-bearing wall 16.The tightening of the belts 34, 35 can be carried out in a similar way,by displacing the generators 30, 31 sideways, as is indicated by theoblong holes 40 in the load-bearing wall 16.

If the wind is weaker than that required to provide half the powerproduction, one of the generators can be disconnected. The possibilityto disconnect half of the generator power means that one can achieve awider regulating range for the wind turbine where there is little wind,than with the help of a single generator and conventional double-fedgenerator control.

Although two secondary shafts and two generators are described in theabove, there is nothing in the way of using several secondary shafts andgenerators. A principle diagram of a system with three secondary shafts23 a, 23 b, 23 c, which by way of the one set of belts 27 is inrotational connection with a large belt disc 21, is shown in FIG. 6.Instead of belts 27, 34, 35, one or more chains that engage with thecogs of the large disc and the secondary shaft can also be used.

Instead of each of the secondary shafts being in connection with theirown generator, these can be rotationally connected with a commongenerator. An example of this is shown in FIG. 7, where the small beltdiscs 25, 26 are connected via a belt disc set 34, 35 to a commongenerator shaft 32 a that goes into a common generator 30 a. Today, thisis the most relevant embodiment.

The way the frame 12 is designed and the way the drive unit ispositioned in the frame, offer good access for inspection andmaintenance. Personnel can come up in the frame 12 via the opening 20,which is in connection with an opening at the top of the tower. Fromhere, the personnel can get to the back of the nacelle via the opening13 and to the front via the opening 18 or 19. Moreover, it is possibleto crawl through the large belt disc 21 itself via one of the openings37 and from here into the hub.

The drive device according to the invention will also be equipped with abrake is which will ensure that nothing rotates while there are peoplein the nacelle. This brake will most appropriately be arranged at thetwo small belt discs or on the generators and be active until themaintenance personnel have manually locked the large belt disc and thehub.

1. A drive device for a wind turbine comprising: a large belt discarranged on a main shaft and at least one belt to transmit rotation fromthe large belt disc to a generator, the large belt disc being inrotational connection with at least two secondary shafts which arearranged in parallel with the main shaft; wherein said secondary shaftsare in turn rotationally connected to at least one electrical generator;wherein the rotational connection between the large belt disc and the atleast two secondary shafts is via the at least one belt; and wherein theat least one belt extends continuously around the large belt disc andthe at least two secondary shafts.
 2. The drive device according toclaim 1, comprising two or three secondary shafts.
 3. The drive deviceaccording to claim 2, wherein the secondary shafts are arranged aroundthe large belt disc at the same angular distance in relation to eachother.
 4. The drive device according to claim 1, wherein the large beltdisc and the main shaft are integrated into each other.
 5. The drivedevice according to claim 1, wherein the secondary shafts arerotationally connected to their individual generators.
 6. The drivedevice according to claim 1, wherein the secondary shafts arerotationally connected to the same generator.
 7. The drive deviceaccording to claim 1, wherein the large belt disc has largethrough-going openings in parallel with the main shaft.
 8. The drivedevice according to claim 1, wherein the drive device is arranged in aframe which provides mounting for the large belt disc, the main shaft,the secondary shafts and the generators.
 9. The drive device accordingto claim 8, wherein the secondary shafts are mounted so that they can bedisplaced sideways in the frame in relation to the main shaft and thelarge belt disc so that tightening of the belt can be adjusted by movingthe secondary shafts.
 10. The drive device according to claim 8, whereinthe frame comprises openings which provide access for maintenance whenthe drive device is arranged in a nacelle on a wind turbine as the framehas an opening towards a tower in which the nacelle is placed and thatthere are openings which give access through both ends of the frame,forwards via openings in the disc and the frame and backwards viaopenings in the frame.
 11. The drive device according to claim 8,wherein the frame comprises a load-bearing wall that provides mountingfor one of the ends of the main shaft and the secondary shafts.